Accurate perception and action depend on the ability of brain attention systems to focus on the most relevant subset of stimuli in the environment. Attention can be directed in a voluntary (top-down) manner, or it may be captured reflexively either by salient sensory stimuli (sensory-driven reflexive attention) or by implicit memories (memory-driven reflexive attention). The experiments proposed here will test current theories and neural models of attentional control by investigating the brain mechanisms supporting each of these types of attention (voluntary, sensory-driven, and memory-driven). Since the momentary focus of attention is normally determined by the interplay between voluntary and reflexive systems, a further objective of these studies is to elucidate the interactions between these attention systems in the brain.In these experiments, event-related brain potentials (ERPs) will be recorded to provide a measure of the timing of neural activity relating to the control of attention and its subsequent effects on visual processing. Functional magnetic resonance imaging (fMRI) will be used to identify the brain regions involved in these attention mechanisms. In these studies: (1) We will investigate the neural mechanisms and temporal dynamics involved in voluntarily shifting the focus of attention. (2) We will directly contrast voluntary attention and sensory-driven reflexive attention, testing both the potential overlap in neural control systems as well as the differential effects of this control on subsequent visual processing. (3) We will investigate the combined versus competitive effects of voluntary and sensory-driven reflexive attention on visual cortical processing. (4) We will investigate the neural mechanisms of "attentional control settings" (ACS) -- task-dependent non-spatial strategic processes that have been shown to modulate the behavioral effects of reflexive attentional orienting. (5) We will test the hypothesis that these ACS share a common pool of mental resources with voluntary attention and working memory, and that under high levels of cognitive load, ACS will not modulate the effects of reflexive attention. (6) We will test whether reflexive orienting driven by implicitly learned predictive relationships modulates subsequent processing as early as does sensory-driven reflexive attention. (7) Finally, we will investigate the neural mechanisms by which memory, specifically item familiarity, reflexively captures attention. We will test the extent to which this type of attention relies upon brain mechanisms thought to underlie voluntary or sensory-driven reflexive attention. Voluntary and reflexive attention mechanisms support a variety of essential human behaviors that, when compromised by damage or disease, have significant impact on human health and the quality of life. Elucidating the brain mechanisms that support the control of attention holds promise for enhancing the understanding, diagnosis and treatment of attentional deficits that are key components of a variety of mental disorders.